Structural control of floating offshore wind turbines with inerter-based low-order mechanical networks

This paper investigates the load mitigation problem for a barge-type floating offshore wind turbine with inerter-based structural control, where a tuned mass damper and an inerter-based mechanical network are employed. The inerter-based mechanical network is the controller to be designed via the fixed-structure method and the network synthesis method. Due to the influence of the wind turbine structure on the wind and wave inputs, improved wind and wave models are proposed. Then by solving an optimization problem with the proposed performance objective function, better element parameters can be obtained. It is shown that the tower-top fore-aft deflection and the tower bottom bending moment of the wind turbine are decreased while the TMD stroke is increased by using an inerter-based low-order mechanical network as controller. After analyzing the performance of different inerter-based low-order mechanical networks, it is found that the controller configurations with an inerter and a spring in series are more conducive to the reduction of the tower-top fore-aft deflection. In addition, the results show that more effective mechanical network configurations for reducing the tower-top fore-aft deflection can be obtained by using the network synthesis method. Finally, a nonlinear aero-elastic simulation tool for wind turbines called FAST-SC is used to verify the above conclusions obtained by a simplified linear model.